Rebel forces have entered the last government-held city in mineral-rich eastern Democratic Republic of Congo, in an offensive that has forced thousands to flee across the border into Burundi, residents say. Heavy artillery and gunfire could be heard in Uvira, with terrified residents describing the situation as chaotic. The escalation in fighting comes despite the peace deal brokered by US President Donald Trump last week between DR Congo's President Félix Tshisekedi and Rwanda's Paul Kagame to end the long-running conflict. The M23 rebel group said it had 'liberated' the city, while UN-backed Radio Okapi quoted residents as saying that rebel fighters were on major streets. However, South Kivu Governor Jean-Jacques Purusi told local media that the army and allied militia remained in control of the city, which is just 27km (17 miles) from Burundi's capital, Bujumbura, across Lake Tanganyika. Burundi has shut its border with DR Congo, a Burundian military source was quoted as saying by AFP news agency. One resident told the BBC that armed M23 fighters had marched in a single column into Uvira from the north-east on Wednesday, meeting no resistance. Some residents cheered their arrival, the resident said. The city was in lockdown, with shops and schools closed as most people stayed indoors. 'Three bombs have just exploded in the hills. It's every man for himself,' one resident told AFP, while another added: 'We are all under the beds in Uvira - that's the reality.' A local rights official told AP news agency that there was a 'risk of a massacre' if the remaining soldiers mounted strong resistance. 'It's chaotic, nobody's in charge. Uvira is done for,' a Burundian officer told AFP. Military and security sources said the rebel fighters advanced from the north, near the Burundian border. The latest offensive comes nearly a year after the M23 rebels seized control of Goma and Bukavu, the other two main cities in eastern DR Congo. About 200,000 people have fled their homes in eastern DR Congo since the latest round of fighting started early this month, the UN says.